Ag-Cu Alloy Research Articles

The interfaces of Ag-rich and Cu-rich AgCu phases boost oxygen reduction activity

In this study, we demonstrated that the interface between Ag-rich and Cu-rich AgCu phases enhances the oxygen reduction activity of the model alloys. Ag-rich and Cu-rich AgCu alloys (86.8 and 4.5 at. % of Ag, respectively) displayed the homogeneous microstructure representing solid solutions while the AgCu with eutectic composition (59.7 at. % of Ag) showed a typical lamellar structure of Ag-rich and Cu-rich AgCu phases. The eutectic AgCu alloy exhibited better oxygen reaction activity than Ag-rich AgCu alloy despite less phase fraction of Ag-rich AgCu phase. After the activation process, the presence of a CuO layer at the interface of the Ag-rich and Cu-rich AgCu phases was discovered by atom probe tomography analysis. Density functional theory calculations further revealed that the preferential adsorption of OH near the interface between CuO and Ag-rich AgCu lowers the binding strength of OH in the Ag-rich AgCu phase. As a result, the oxygen reduction activity was enhanced by facilitating the most sluggish OH desorption step. These findings provide new insights into the role of phase boundaries in catalytic activity and guidelines for the design of novel electrocatalysts.

Quantifying the optical and thermoplasmonic properties of some bimetallic alloy nanospheres

The bimetallic alloy NPs are ideal objects for a variety of applications like catalysis, nanofluidics, thermo-voltaic and bio-imaging due to their peculiar and adaptable optical response in UV–visible-NIR region of optical spectra. The heating effect of bimetallic alloys involves surface plasmon resonance (SPR) and takes place when the material is illuminated by light. Instead of pure and alloy NPs of Au & Ag, the opto-thermal properties of Au-Cu, Au-Al, Ag-Cu and Ag-Al bimetallic alloy nanospheres for their different compositions with a size radius of 10 nm to 50 nm immersed in water (n = 1.33) using the Mie theory approach are investigated theoretically. In order to determine the heat generation and the temperature distribution by plasmonic nanoparticles in the host medium (water in this study) we have solved the heat transfer equation analytically for steady-state conditions. The great utility of these bimetallic alloy nanoparticles for thermoplasmonic investigation is accompanied with a large extent of SPR tunability which is rarely found in their pure monometallic counterpart. The SPR of Aux-Cu1-x (214 nm to 548 nm), Aux-Al1-x (213 nm to 493 nm), Agx-Cu1-x (214 nm to 539 nm), and Agx-Al1-x (214 nm to 381 nm) bimetallic alloys with compositions of x = 0.25,0.50 and 0.75 have been observed for different size of the nanospheres. Thus, we anticipate that the results of this work will evoke the curiosity of researchers towards the use of bimetallic alloys in thermoplasmonic applications.

Reaction-Driven Formation of Ag-Cu Alloy Nanostructures from Cu@Ag Core-Shell Nanoparticles Analyzed by Moirè Patterns Using Environmental TEM Images

Well defined Cu@Ag core@shell (or core-shell) nanoparticles have been synthesized through a carbon monoxide (CO)-assisted solution phase method. These Cu@Ag nanoparticles transformed into Ag-Cu alloy nanostructures under propylene epoxidation conditions. Environmental transmission electron microscopy (ETEM) revealed the structural evolution of Cu@Ag nanoparticle under different propylene-to-oxygen (PP/O2) ratios based on the Moirè pattern analysis of the micrographs obtained in situ. The counter diffusion of Ag and Cu atoms, from the shell and core respectively, was observed at the PP/O2 ratio of 2:1. When the PP/O2 ratio was 1:1, Cu@Ag core-shell nanoparticles turned into alloy nanostructures. The transformation from Cu@Ag to Ag-Cu alloy nanoparticles changed the catalytic performance in the production of propylene oxide from partial oxidation of propylene, resulting in a yield of 1.14 min−1 and selectivity of 79% when the PP/O2 ratio was 2:1. This study shows besides temperature and pressure, other less-studied factors of reaction conditions such as composition of reactants may play critical roles in the dynamics of bimetallic nanostructures, thus their corresponding catalytic performances. This study develops the techniques on the applications of Moirè patterns for analyzing the dynamics of bimetallic core-shell nanostructures at atomic scale using (S)TEM micrographs.

Thermally stable threshold selector based on CuAg alloy for energy-efficient memory and neuromorphic computing applications

As a promising candidate for high-density data storage and neuromorphic computing, cross-point memory arrays provide a platform to overcome the von Neumann bottleneck and accelerate neural network computation. In order to suppress the sneak-path current problem that limits their scalability and read accuracy, a two-terminal selector can be integrated at each cross-point to form the one-selector-one-memristor (1S1R) stack. In this work, we demonstrate a CuAg alloy-based, thermally stable and electroforming-free selector device with tunable threshold voltage and over 7 orders of magnitude ON/OFF ratio. A vertically stacked 64 × 64 1S1R cross-point array is further implemented by integrating the selector with SiO2-based memristors. The 1S1R devices exhibit extremely low leakage currents and proper switching characteristics, which are suitable for both storage class memory and synaptic weight storage. Finally, a selector-based leaky integrate-and-fire neuron is designed and experimentally implemented, which expands the application prospect of CuAg alloy selectors from synapses to neurons.

Novel SiC-Based Power Device Bonding Materials of Nano Foam Sheet and Its Characteristic and Properties

Silicon carbide (SiC) has excellent characteristics such as high thermal and electrical conductivity. However, traditional bonding materials are difficult to serve lastingly at high temperature, which directly affects the performance of SiC-based devices. In this study, nano foam sheet was prepared by dealloying, and used to sinter chip and substrate at low temperature. Microstructure, interfacial composition, mechanical properties and fracture of the sintered joint were characterized and analyzed. The precursor was AgCu alloy, and the bicontinuous ligament/channel structure was formed on the precursor surface after dealloying. As the etching temperature increased from 80 °C to 90 °C, the ligament width of nano foam became large and channel diameter became small. With the extension of etching time from 2 h to 5 h, the etching depth gradually increased. The nano foam sheet could realize metallurgical reaction between substrate and chip at a sintering temperature of 300 °C. The joint had high shear strength, and could meet the strength requirement of standard.

Temporal Aspects of Corrosion Inhibition on Copper, Silver, and Copper-Silver Alloys: An Electrochemical Impedance Spectroscopy Study

Electrochemical impedance spectroscopy (EIS) was utilized to delve into the corrosion inhibition of eutectic Cu-Ag alloy and its components (Cu and Ag) in an aqueous, aerated 0.1 M KNO3 solution. This alloy plays a major role in the water cooling of central processing units in data storage centers. Two organic inhibitors, namely, 1,2,3-benzotriazole (BTA) and 2,5-dimercapto-1,3,4-thiadiazole (DMTD), were utilized in this study. The corrosion inhibition slowly evolved over time as diagnosed by an increase in the charge transfer impedance and the gradual tendency of the Nyquist profiles to arc toward the real axis. This trend was attributed to the gradual formation of organometallic passivation layers. The EIS data underlined the specific affinity of BTA and DMTD toward the Cu and Ag surfaces, respectively. A transition of the double-layer equivalent circuit element from ideal capacitance to a constant phase element was observed for the alloy compared to the pure metals. This was attributed to the heterogeneity induced by Cu-rich and Ag-rich phases in the alloy and by the formed oxides/protective film on the alloy surface. The EIS study demonstrated that both BTA and DMTD can provide sufficient corrosion inhibition to Cu-60Ag alloy with DMTD being significantly more effective.

Exploring the Influence of the Coarse Grain Size and Ag Atomic Content on Mechanical Properties of Bimodal Nanotwinned Cu-Ag Alloys

Exploring the Influence of the Coarse Grain Size and Ag Atomic Content on Mechanical Properties of Bimodal Nanotwinned Cu-Ag Alloys

A potential recyclable catalyst: In situ growth of bimetallic Cu-Ag nanoalloy on the magnetic SiO2/Fe3O4-SiO2-NH2 nanocomposite support using a green approach

In this study, bimetallic Cu-Ag alloy nanoparticles (NPs) are anchored on the surface of magnetic functional SiO2/Fe3O4-SiO2-NH2 nanocomposite support using glucose as a green reducing agent. SiO2/Fe3O4-SiO2-NH2 nanocomposite support is prepared in one-pot via simultaneous co-precipitation of iron salts and alkaline hydrolysis-condensation reaction of tetraethyl orthosilicate (TEOS) in presence of SiO2 sphere. Hexamethylene diamine (HMDA) and cetyltrimethylammonium bromide (CTAB) are used as functional agent and structure directing agent, respectively. Finally, Cu-Ag NPs are formed on the functional nanocomposite support via in-situ green reduction protocol to obtain SiO2/Fe3O4-SiO2-NH2/Cu-Ag nanocatalyst. A comparative study of catalytic reduction of 4-nitrophenol (4-NP) to 4-aminophenol (4-AP) showed that calcined SiO2/Fe3O4-SiO2-NH2/Cu-Ag nanocatalyst possessed higher reduction kinetics compared to corresponding non-calcined nanocatalyst. Similar enhancement in catalytic property for unsupported bimetallic Cu-Ag NPs is noticed after calcination. The incorporation of magnetic Fe3O4 in the SiO2/SiO2-NH2 support material also considerably enhanced the catalytic property of the nanocatalyst. The reduction reaction favorably followed pseudo-first-order kinetic rate model and the rate constants of non-calcined and calcined SiO2/Fe3O4-SiO2-NH2/Cu-Ag nanocatalysts are 0.0517 and 0.0998 min−1, respectively. The magnetically separable non-calcined SiO2/Fe3O4-SiO2-NH2/Cu-Ag nanocatalyst is recyclable up to five cycles with fairly acceptable conversion.

Bimetallic Ag-Cu Alloy SERS Substrates as Label-Free Biomedical Sensors: Femtomolar Detection of Anticancer Drug Mitoxantrone with Multiplexing.

Surface-enhanced Raman spectroscopy (SERS) has been recognized as a promising label-free technology for clinical monitoring due to its high sensitivity and multiplexing ability, which should accelerate the screening of important drugs in the blood and plasma of cancer patients in a simpler, faster, and less-expensive manner. In this work, bimetallic Ag-Au and Ag-Cu alloy microflowers (MFs) with tunable surface compositions were fabricated on a glass cover slip by simple thermolysis of a metal alkyl ammonium halide precursor and used as SERS substrates for the sensitive detection of anticancer drug mitoxantrone (MTO). Two different laser excitation sources, 532 and 632.8 nm, were used to explore the possibility of surface-enhanced resonance Raman scattering. The Ag-Cu substrate showed superior detection capability over Ag-Au, whereby the sensor recorded a noteworthy "limit of detection" value of 1 fM for MTO. Theoretical electromagnetic field maps were simulated on appropriately chosen plasmonic systems to compare the electromagnetic field enhancements with the experimental SERS efficiencies of the substrates. Further, using a 10% Ag-Cu substrate, efficient multiplexing detection of MTO was demonstrated with another anticancer drug doxorubicin (DOX) in water and mouse blood plasma.

Reforming nanostructured CuAg alloy to improve ductility and electrical conductivity

Nanostructured metallic materials often lack sufficient work-hardening capability and suffer premature necking during tensile loading. In this study, intense rolling strain was applied to process nanocrystalline CuAg sheet, and aging treatment was designed to further tailor the microstructure and properties. Features of grains, Ag precipitates and short-range ordered (SRO) structure were characterized by transmission electron microscope (TEM). Superior tensile strength of 600 MPa, uniform elongation of 10% and electrical conductivity of 86.7% IACS were successfully achieved. Mechanisms for the balanced mechanical and electrical properties were analyzed.

Effects of Indium and Gallium ratio on tarnish resistance, corrosion and mechanical properties of 950 silver alloy

The effects of Indium (In) and Gallium (Ga) ratio on tarnish resistance, corrosion and mechanical properties of 950 silver alloy were studied. 950 Silver alloy with aluminium (Al), silica (Si) and germanium (Ge) were added with In and Ga at the range of 0.44 to 1.90 weight percent. The increment of secondary structure with Ge-Si rich phase in Ag-Al alloy increases hardness, but reduces ultimate tensile strength. The addition of In and Ga improves tarnish and corrosion resistance. The color differences as indicated by Delta E tolerances (DE*) of Ag-Al alloys are in the range of 8.64 to 11.40 while this property of Ag-Cu is 39.37. Ecorr of Ag-Al alloys are in the range of -0.068 to -0.010 V which are higher than that of Ag-Cu Alloy (-0.147 V). Besides, Ga is more effective for tarnish and corrosion resistance than In. However, Ga/In co-addition reduces these properties by the formation of Ge-Si-Ga-In phase. The protective thin film of Ag-Al alloy was detected by XPS. The Al2O3, In2O3 and Ga2O3 films were found. When the proportion of Ga in Ag-Al alloys increases, the hardness marginally increases while the tensile strength slightly reduces. The additions of Al, Ga, In, Ge and Si reduce the melting point of Ag-Al alloys comparing with Ag-Cu alloy and simultaneously improve the casting quality.

The Tunable and Efficient Nanoporous CuAg Alloy Catalysts Toward Methanol Oxidation Reaction Synthesized by Electrochemical Dealloying of Metallic Glassy Precursors.

Three-dimensional (3D) nanoporous CuAg (NPCuAg) alloy catalysts with various Cu/Ag ratios are prepared by electrochemical dealloying of metallic glassy (MG) precursors. All dealloyed samples exhibit homogenous nanoporous structure and element composition distribution. After systematically evaluating their electrocatalytic performance toward MOR, it was found that the catalytic activity of the NPCuAg catalysts is enhanced along with the increase of Cu/Ag ratio, which may be attributed to the more exposed active reaction sites derived from high surface area of nanoporous structure and the optimal synergistic effect. Thus, the NPCu1.75 Ag alloy catalyst presents the best methanol electro-oxidation properties, including a high current density of 397.2 mA cm-2 and good operation stability that retaining 84.5 % catalytic activity even after 7200 s. These results outperform most reported copper-based MOR catalysts in alkaline methanol solution. Considering these advantages, the designed electrodes are expected to be promising catalysts for alkaline DMFCs applications.

A Study on the Composition and Manufacturing Technology of Rivets in Bronze Objects

To completely bond two or more metals, there is a method of applying heat or using a nail. Most bronze containers use nails to bond and repair, which are called rivet techniques. Until now, the manufacturing technology of bronze ware has been conducted by many researchers, but research on rivets used in bronze ware is insufficient. In order to understand the manufacturing technology of bronze ware, research on not only the main body of the container but also each part must be conducted together. In the case of rivets, it is believed that they were made in consideration of the material, color, and economic feasibility suitable for the Bronze Age, and in this study, metallic analysis was conducted focusing on the four rivets excavated. As a result of metal microscope and SEM-EDS analysis, it is judged that the Cu-Sn-Pb ternary alloy and Cu-Ag binary alloy were manufactured using the general casting method. Compared to previous studies, rivets can be divided into (1) 100% pure copper (Cu) (2) Cu-Sn-Pb ternary alloys (Sn, Pb around 10%), and (3) Cu-Ag binary alloys, and this time the analyzed rivets correspond to types (2) and (3). If you study not only rivets but also containers in the future, it will be helpful to understand the manufacturing technology process of bronze containers.

A comparative study of Cu-Au, Ag-Au and Ag-Cu alloys: A pseudopotential approach

Using the pseudopotential approach, we have calculated the mechanical characteristics of the alloys Cu-Au, Ag-Au, and Ag-Cu. We have employed pseudopotentials due to Pandya et al. (Physica B, 2001;307:138–149) and Bhatia et al. (Philos. Mag., 2021;101(13): 1602–1618) to calculate PDC (Phonon dispersion curves), P-DoS (Phonon density of states), WT (Debye-Waller factor), u¯2 (mean square displacement), heat capacity (CP), elastic constants (C11, C12 and C44), bulk modulus (B) and anisotropic factor (A). In the absence of experimental research, theoretical findings of PDC for alloys AgAu3 and AgCu3 (excluding CuAu3) are provided for the first time, which may be used to estimate the comprehensive physical characteristics. Our elastic constants findings agree with existing experimental results. These pseudopotentials have been found successfully for the study of solid as well as liquid metal properties.

Suppression of discontinuous precipitation and strength improvement by Sc doping in Cu-6 wt%Ag alloys

• Sc doping significantly suppressed discontinuous Ag precipitates in Cu-Ag alloys. • Sc-doping led to a 55 MPa increase in strength, with only a slight decrease in conductivity. • Sc segregation at grain boundaries inhibited the nucleation of discontinuous precipitates • The UTS of Sc-doped samples was 1080 MPa, 205 MPa higher than that of non-doped samples. In low-Ag Cu matrix alloys, the presence of coarse discontinuous precipitates may limit strength. We demonstrated that discontinuous precipitation was suppressed, and continuous precipitation was enhanced by the doping of Cu-6 wt%Ag with Sc. A high-volume fraction of continuous precipitates, which nucleated on {111} planes, led to a 55 MPa increase in strength, with only a slight decrease in electrical conductivity. The addition of Sc inhibited the nucleation of discontinuous precipitates by causing the Sc and the Ag to co-segregate onto grain boundaries, thus forming a thin intermetallic compound layer between grains. After deformation, both discontinuous and continuous precipitates were drawn into Ag fibers. The combination of deformation strain and doping caused an increase in density and a decrease in the diameter of Ag fibers, resulting in about 205 MPa increase in doped samples when the deformation strain reached 4.9. The thinner, denser Ag fibers in the doped samples also caused higher electron scattering at interfaces, leading to electrical conductivity that was 11% IACS lower than in non-doped samples. For reference, 100% IACS (International Annealed Copper Standard) is equivalent to 1.7241 μΩ cm.

Effect of Size on the Formation of Solid Solutions in Ag-Cu Nanoparticles.

Modern technologies stimulate the quest for multicomponent nanosized materials with improved properties, which are ultimately defined by the atomic arrangement and interphase interactions in the nanomaterial. Here, we present the results of the experimental study of the formation of solid solutions in Ag-Cu nanoparticles in a wide size and temperature range using in situ TEM techniques. The Ag-Cu nanoparticles with a eutectic ratio of components were formed on an amorphous carbon film by the physical vapor deposition technique. Electron diffraction, HAADF-STEM imaging, energy-dispersive X-ray spectroscopy, chemical element mapping, and electron energy loss spectral imaging were used for the characterization of mixing patterns and composition of phases in AgCu nanoparticles down to the atomic level. As a result, we constructed the solid-state part of the Ag-Cu phase diagram for nanoparticles with a size down to 5 nm. We found a highly asymmetric behavior of the solvus lines. Thus, the content of Cu in Ag gradually increased with a size reduction and reached the ultimate value for our configuration of 27 wt % Cu at a nanoparticle size below ∼8 nm. At the same time, no Cu-rich solid solution was found in two-phase AgCu nanoparticles, irrespective of the size and temperature. Moreover, a quasi-homogeneous solid solution was revealed in AgCu nanoparticles with a size smaller than 8 nm already at room temperature. A size dependence of the terminal temperature T term, which limits the existence of AgCu alloy nanoparticles in a vacuum, was constructed. Evaporation of the AgCu phase with the composition of 86 wt % Ag was observed at temperatures above T term. We show the crucial role of the mutual solubility of components on the type of atomic mixing pattern in AgCu nanoparticles. A gradual transition from a Janus-like to a homogeneous mixing pattern was observed in Ag-Cu nanoparticles (28 wt % Cu) with a decrease in their size.

Induction brazing of NdFeB magnet with PVD-deposited AgCu alloy

The NdFeB magnets service in high-power electric-mechanical conversion devices sometimes endure high stress and high-temperature impact, and adhesion of these magnets using glue cannot ensure the reliability. In this study, the NdFeB was induction brazed with physical vapor deposition (PVD)-deposited Ag72Cu28 alloy layer, then the microstructure, mechanical properties and magnetic properties of the brazed joints were characterized, and effects of the filler metal thickness and the induction heating time were analyzed. The results show that the PVD coating can effectively prevent the surface oxidation of the NdFeB. The AgCu filler metal penetrates into the NdFeB and is partly mixed with the liquefied Nd-rich intergranular phase of the NdFeB, forming a good metallurgical bonding. The thickness of the penetration layer increases obviously with increase of the heating time and filler metal thickness. The bonding strength of the NdFeB brazed joint increases firstly and then decreases with increasing heating time, and a peak bending strength of 196.94 MPa was obtained. Fracture of the brazed joint occurs inside the NdFeB substrate close to the penetration layer. After a further annealing, the coercivity of the brazed NdFeB sample is a little higher than that of the un-brazed sample, and the squareness decreases by only a little. Properties of the brazed joints might be further improved by optimizing the amount of filler metal and the induction heating parameters.

Long-sliding distance experiment and heuristic model prediction of the electrical sliding abrasion of an overhead wire/current collector

Several long-sliding distance tests on the electrical sliding abrasion of an overhead wire/current collector were performed on a test rig. The test parameters cover electric currents of DC 0, 100, 200, 300, 400 A, normal force of 15, 25, 35, 45 N, sliding speeds of 60, 80, 100 km/h, and sliding distance of 6000 km. Test results illuminate that the electric current significantly impacts the electric sliding abrasion performance of the Cu-Ag alloy overhead wire and current collector. Its main wear mechanisms involve adhesive, plowing, electrical, and arc wears. Bucca and Collina’s wear prediction models of overhead wires and current collectors were established using the obtained wear test data. More parameter sensitivity analyses were carried out using the wear prediction models.

Single atom alloy clusters Agn-1X- (X = Cu, Au; n = 7-20) reacting with O2: Symmetry-adapted orbital model.

Single atom alloy AgCu catalysts have attracted great attention, since doping the single Cu atom introduces narrow free-atom-like Cu 3d states in the electronic structure. These peculiar electronic states can reduce the activation energies in some reactions and offer valuable guidelines for improving catalytic performance. However, the geometric tuning effect of single Cu atoms in Ag catalysts and the structure-activity relationship of AgCu catalysts remain unclear. Here, we prepared well-resolved pristine Agn - as well as single atom alloy Agn-1Cu- and Agn-1Au- (n = 7-20) clusters and investigated their reactivity with O2. We found that replacing an Ag atom in Agn - (n = 15-18) with a Cu atom significantly increases the reactivity with O2, while replacement of an Ag with an Au atom has negligible effects. The adsorption of O2 on Agn - or Agn-1Cu- clusters follows the single electron transfer mechanism, in which the cluster activity is dependent on two descriptors, the energy level of α-HOMO (strong correlation) and the α-HOMO-LUMO gap (weak correlation). Our calculation demonstrated that the cluster arrangements caused by single Cu atom alloying would affect the above activity descriptors and, therefore, regulates clusters' chemical activity. In addition, the observed reactivity of clusters in the representative sizes with n = 17-19 can also be interpreted using the symmetry-adapted orbital model. Our work provides meaningful information to understand the chemical activities of related single-atom-alloy catalysts.

A bimetallic Ag15Cu12(S-c-C6H11)18(CH3COO)3 nanocluster featuring an irregular Ag12 kernel.

Here, we report the synthesis and atomic structure of a Ag15Cu12(SR)18(CH3COO)3·(C6H14) nanocluster (Ag15Cu12 for short, SR denotes cyclohexanethiol), confirmed by single-crystal X-ray diffraction (SC-XRD), electrospray ionization mass spectrometry (ESI-MS), X-ray photoelectron spectroscopy (XPS) and thermogravimetric analysis (TGA). X-ray crystallographic analysis revealed that Ag15Cu12 consisted of an irregular Ag12 core, stabilized by the Ag3Cu12(SR)18(CH3COO)3 shell. The shell consisted of two nearly planar Cu3(SR)6 moieties, three monomeric [-SR-Ag-SR-] units and three Cu2(CH3COO) staples. Furthermore, time-dependent density functional theory (TD-DFT) simulation was performed to interpret the optical absorption features of Ag15Cu12. Overall, this work will broaden and deepen the understanding of Ag-Cu alloy nanoclusters.